Microsoft on Friday said Windows 10 beta testers will receive a free copy of the operating system's stable build next month then almost immediately tweaked its statement, again muddying the waters.

Gabriel Aul, the engineering general manager for Microsoft's operating system group, got the ball rolling Friday in a blog where he also pointed out several changes to the Windows Insider program, Microsoft's name for its Windows 10 preview regimen. The most newsworthy of Aul's statements was that Insider participants would receive Windows 10's final code, even if they didn't install the preview on a Windows 7 or 8.1 PC eligible for the one-year free upgrade.

"Windows Insiders running the Windows 10 Insider Preview (Home and Pro editions) with their registered MSA [Microsoft Account] connected to their PC will receive the final release build of Windows 10 starting on July 29," Aul said. "As long as you are running an Insider Preview build and connected with the MSA you used to register, you will receive the Windows 10 final release build."

In several tweets Friday, Aul expanded on the deal, which he had alluded to several months ago without spelling out details.

"Genuine" is Microsoft-speak for a legitimate, activated copy of its software. As of Sunday, build 10130 was the most recent of Windows 10; Microsoft released it on May 29.

The move as Aul outlined it would be unprecedented for the Redmond, Wash. company, which has historically turned a deaf ear to suggestions from public beta testers that they be rewarded for their work hunting down bugs with free software.

But while the decision evoked a more generous Microsoft, it was tempered by the reality that most customers running consumer- or business-grade editions of Windows 7 and 8.1 -- with the notable exception of Windows Enterprise, the for-volume-licensing-customers-only SKU (stock-keeping unit) -- will get a free copy of Windows 10 in any case.

The route to a free copy of Windows 10, Aul implied, would be of interest only to users who did not have a genuine-marked copy of Windows 7 Home Starter, Home Basic, Home Premium, Ultimate or Professional, or Windows 8.1 or Windows 8.1 Pro.

Those users would include people who had PCs currently running an ineligible OS, such as Windows Vista or the even older Windows XP, or who want to equip a virtual machine (VM) with Windows 10 on a device running another edition of Windows or, say, a Mac armed with software like VMware's Fusion or the open-source VirtualBox.

Aul's reference to build 10130 may mean that the window of opportunity for the free Windows 10 will shut once that is superseded by the next iteration.

More interesting, however, was an addition to Aul's blog made between its Friday debut and late Saturday: "It's important to note that only people running Genuine Windows 7 or Windows 8.1 can upgrade to Windows 10 as part of the free upgrade offer."

That line was tacked onto the end of the paragraph in which Aul had described the process by which Insider participants would be able to obtain the stable release on July 29, and that all testers -- whether they upgraded from Windows 7 or 8.1 or installed the preview on a wiped drive or VM -- would be able to run Windows 10 free of charge.

The blog post was also edited, removing the word "activated" from the original. The initial post said, "As long as you are running an Insider Preview build and connected with the MSA you used to register, you will receive the Windows 10 final release build and remain activated. Once you have successfully installed this build and activated, you will also be able to clean install on that PC from final media if you want to start over fresh [emphasis added]."

The revamped post deleted the words in bold above.

Microsoft's (or Aul's) changes threw doubt onto the statements Aul had made. He did not reply to a question posed via Twitter late Saturday about whether the process as he outlined still stood.

The removal of "activation" -- and the new line with the term "genuine" in it -- signaled that it did not. The simplest explanation is that while Microsoft will, in fact, give testers the stable build, it will not be activated with a product key, and thus "non-genuine" in Microsoft parlance, unless some other step is taken, perhaps a connection to a prior copy of Windows 7 or 8.1.

Non-genuine copies of Windows are marked as such with a watermark. Microsoft has not revealed what other restrictions might be placed on an unactivated or non-genuine copy of Windows 10.

Interpretation gymnastics are virtually required when parsing Microsoft's statements. Microsoft chooses its words carefully, and when it does disclose information, often does so in parcels that are by turns opaque, ambiguous and confusing to customers. That frequently forces it to retract or modify earlier comments.

Something similar occurred earlier this year when Microsoft seemed to say that non-genuine copies would be upgraded to legitimate versions of Windows 10. Days later the company walked back from that stance, saying that the free Windows 10 upgrade offer "will not apply to non-genuine Windows devices."

The confusion may be frustrating to some customers -- as in many other cases, customers who are among the most vocal of Microsoft's -- but moot for the vast majority of users, who will simply upgrade existing, and eligible, PCs. Microsoft's licensing is complex enough that there are countless edge cases where ambiguity is a side effect.

Still, the lack of clarity about many questions related to Windows 10 at this late date is disturbing, although not rare for Microsoft. At times the company seems entirely unable to come clean about its policies.

Computerworld, for example, installed the 10130 build from a disk image onto a new VM on a Mac -- not as an upgrade from one equipped with Windows 7 or 8.1 -- and although it was marked as "Windows is activated," that may not last.

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